Seasonal response of herbage production and its nutrient and mineral contents to long-term cattle grazing on a Rough Fescue grassland

This study investigated the effect of long-term cattle grazing on herbage production and its nutrient and mineral concentrations over the grazing season. The grazing experiment was conducted on a Rough Fescue (Festuca campestris Rydb.) grassland established in 1949. The three grazing treatments were moderate grazing (MG), heavy grazing (HG), and a non-grazed exclosure (CK) with corresponding stocking rates of 2.4, 4.8, and 0 animal unit months (AUM) ha−1, respectively. Within each of these three treatments four sampling locations were selected as four replications. Herbage biomass (green standing crop [current years’ production] and litter biomass [previous years’ production]) and its nutrient and mineral concentrations were determined monthly from May to September 2007. The green standing crop increased but litter biomass decreased with grazing and peak green standing crop for MG and HG occurred one month earlier than in the CK. For the green standing crop, total nitrogen (TN) concentration increased with grazing from 28.2 g kg−1 in the CK to 39.9 g kg−1 in the HG treatment in May while increases (12.4–15.7%) in other months were not significant. Total phosphorus (TP) (16.4%) and δ15N were higher in the HG than in the CK. For the litter, TN and Ca concentrations decreased with grazing, but TP, δ15N, K and Mg concentrations increased. The herbage feed quality also varied over the grazing season with TN, TP, K, and Mg concentrations decreasing over the grazing season while Ca concentration was lowest in spring (3.07 g kg−1) and late fall (4.08 g kg−1). Grazing appeared to accelerate nutrient cycling and improved herbage quality. These grasslands require disturbance for optimal performance but heavy grazing pressure could severely reduce their health.